PROJECT SUMMARY Summary Head and neck cancer accounts for about 4% of all cancers in the United States with an estimated 64,690 people (47,650 men and 17,040 women) new cases this year. Recently immunotherapy, in the form of immune checkpoint blockade (ICB), is proving to be effective at restoring T cell mediated immune responses that can lead to marked and sustained clinical responses, but only in some patients with cancer ? particularly head and neck cancers. Patients respond unpredictably to immunotherapy partly owing to heterogeneity of the immune composition but mainly due to variation in the number of mutations, with the tumor mutational burden (TMB) strongly correlating with the likelihood of response. There is now overwhelming evidence that mutation-derived neoantigens are targeted by T-cells in tumor control but unfortunately the majority (>80%) of patients with head and neck cancer lack sufficient neoantigens to respond to ICB. A compounding rate limiting factor is the low frequency of tumor-specific immunity which is difficult to detect even in ICB responding patients. In contrast we have found patients with HNSCC have extremely high levels of immunity against persistent viruses which can be over 50% of CD8+ T-cells. Yet this immunity is unable to participate in targeting cancer cells due to the exquisite specificity of the T-cell receptor (TCR). Currently, there are no mechanisms to alter or increase antigens in cancer. We hypothesize that by selective delivery of highly immunogenic peptide antigens, we can reprogram tumor cells to strongly engage with pre-existing cytotoxic T-cells. In a recent advance from our laboratory, we have been able to selectively reprogram tumor antigenicity through the release of MHC class-I restricted peptide antigens, delivered using antibodies. We have developed antibody peptide-epitope conjugates (APECs) can selectively deliver peptides to the cell surface that then passively surface-load into empty MHC class-I molecules without becoming internalized. Based on preliminary results, we propose to develop a biotherapeutic that is able to modulate the antigens displayed on HNSCC, to match tumor antigenicity with preexisting CTL repertoire. With support through this P01 grant, we aim to develop and test a new immunotherapeutic approach for treating TMB low head and neck cancer. The specific aims of the study are:- (1) map anti-viral immunity in patients with HNSCC and then design APECs that efficiently and selectively reprogram MHC class-I molecules to present leading viral antigens; (2) Understand the in vivo constraints of antigenic reprogramming and test synergy with ICB and epigenetic modulation via 5'azacytidine to redirect human anti-viral immunity against human HNSCC in vivo.